The invention relates to a method for producing a piston ring made of cast iron or cast steel.
It is generally known to provide piston rings with wear-resistant layers. In many instances, very hard PVD (physical vapor deposition) layers are deposited on the running face. It is known from engine operation that piston rings, in particular in the first groove, at the joint are subject to greater wear than at the ring back. At the same time, the PVD layer impairs the radial pressure distribution of the ring during engine operation. Due to the differing thermal expansion of the coatings and the base material (bimetallic effect), the pressure at the joint increases, thereby favoring even higher wear in this region. This also results in a higher load on the counter-body, and consequently also in higher wear on the same.
JP 2001-295699 A1 discloses a piston ring comprising a coated running face. The running face of this piston ring is provided with a hard PVD layer. A further layer is deposited on the same, which has improved running-in properties than the hard PVD layer. This measure is intended to provide optimized pressure distribution, seen in the circumferential direction of the piston ring, since the running-in layer is ablated relatively quickly in the region of the piston ring close to the joint.
EP 1 359 351 B1 relates to a generic method. A base body provided with a joint is caused to rotate and is rotated around an evaporation source. Differing layer thicknesses are created, looking at the circumference of the base body, as a result of differing rotational speeds. The layer thickness in the joint region should be larger than in the remaining circumferential region.